1. Field of the Invention
The present invention relates to a communication control device in a computer system. The system according to the present invention is used for communication control in a distributed type electronic computer system connected through networks including, for example, data bus, loop transmission line, and the like
2. Description of the Related Arts
In general, in an inter-computer communication, a communication protocol is used for carrying out the detection and correction of errors in communication data and for controlling of the flow of communication data between a transmitting side and a receiving side. In the communication protocol, an analysis of destination address information, data sequence information, and communication command is carried out. Such an operation is generally realized by software control.
Assuming that a plurality of computers are interconnected via a plurality of communication control devices and a network, then in general, in accordance with a request for transmitting at a communication control device as a transmitting node, communication data is transmitted in the form of a communication data frame from the transmitting node, based on a predetermined protocol processing. Upon receipt of this communication data frame by the receiving node, a response processing of this communication data frame is carried out at the receiving node.
When the receipt at the receiving node is a normal receipt, "ACK" information, which is acknowledge information, is returned to the transmitting node, and the communication data is transmitted, to a higher order computer to complete the receiving. On the other hand, when the receipt at the receiving node is an abnormal receipt, "NAK" information, which is negative acknowledge information, is returned to the transmitting node. At the transmitting node which receives "NAK" information, a response data inspection process is carried out. When the response data is "NAK", a re-transmitting process of the corresponding communication data is carried out, and when the response data is "ACK", the transmitting is completed.
In general, a communication control device as a node, collects communications from a plurality of computers, and must carry out a plurality of transmitting and receiving processing operations. If n transmitting operations are carried out by a communication control device, the communication control device will receive n response signals, each of which is either ACK or NAK. There are differences between receiving processing time in receiving nodes, and between delays in communications in the network. Accordingly, the returns of the response data are carried out independent of the order of the transmitting of the communication control device. As a result, transmitted communication data does not necessarily have a time-correspondence relationship with the corresponding response data. Thus, it is necessary to arrange the transmitted communication data and the received response data in a time-correspondence relationship. Therefore, it is necessary to search the communication control table in which the communication control information is stored.
Under these circumstances, if the number n of the above-mentioned transmitting processings is large, the time-length required for the search becomes considerably long and cannot be neglected. Hence, the speed of operation of the device is lowered. This constituents a disadvantage of the prior art. In many cases, the above-described search is carried out by software. Assuming that the time required for a search and comparison of one entry of a communication control table by software is Tc, the time required for a search and comparison of one entry out of n entries in the binary search algorithm will be, on average, log.sub.2 n.times.Tc. Assuming that the instruction required for search and comparison concerning 1 entry is constituted by five computer instructions, and a computer having a processing speed of 10.sup.6 instructions/sec is used, the time length required for the search will be 5.times.log.sub.2 n.times.10.sup.-6 sec; i.e., this time length required for the search will be 40 .mu.sec for n=256. This long time length required for a search constitutes a disadvantage of the prior art.